Ferrous metal



June 9, 1964 J, c. ELLIOTT 3,136,656

METAL SURFACING METHOD Filed March 13, 1961 ARTICLE DRIED ZZ: STAGE 2 5 FIG. I

ARTICLE HEATED 2 TO DULL RED STAGE 3 INCANDESCENCE \|1, \\\\\m//// ARTICLE COOLED TO AMBIENT STAGE 4 TEMPERATURE INVENTOR. JOHN C. ELLIOTT Li. M

ATTORNEY United States Patent f 3,136,656 METAL SURFACING METHOD John C. Elliott, Anaheim, Calif., assignor to Lor Corporation, Enid, Okla, a corporation of Delaware Filed Mar. 13, 1961, Ser. No. 95,182 7 Claims. (Cl. 117-127) This invention relates to a method for surface treating ferrous metals and more particularly relates to a process for treating ferrous metal to render it resistant to chemical and physical attack at elevated temperatures in corrosive environments.

This is a continuation-in-part application of United States patent application Serial No. 629,785 of the same entitlement and inventorship filed December 21, 1956, now abandoned.

Small tools and industrial equipment are quickly corroded by molten metal especially when the tool or equipment is abraded or is rotated in the molten metal. Corrosion-resistant steel alloys are usually utilized as construction materials for such tools and equipment, but even these materials are rapidly consumed by molten metals such as aluminum.

It has been known to prepare tools and equipment for use in molten metals by calorizing. In this method an article is immersed in a mixture of aluminum powder,

alumina, and a small portion of ammonium chloride in v substrate.

3,136,656 Patented June 9, 1964 terial is clad onto a substrate. An unheated salt solution is a less expensive treatment material than is granulated or atomized metal, and the energy consumed in the treatment is less than that consumed in the abovedescribed processes wherein the material must be heated to high temperature both before and after treatment.

No dimensional change is produced herein and the process may be used to treat delicately balanced or high speed rotative components as well as other closely dimensional articles.

It is an object of this invention to provide a process for protecting metal objects from the corrosive effects produced by molten metal.

' It is another object of this invention to provide a less expensive method for surface treating ferrous metals than those now known.

Other objects will become apparent from the drawing and from the following detailed description in which it is intended to illustrate the applicability of the invention without thereby limiting its scope to less than that of all equivalents which will be apparent to one skilled in the art.

. FIGURE 1 is a flow diagram of the process of this invention.

In heretofore known processes wherein aqueous aluminum chloride solution has been used as a dip bath for an article which is to be dried and heated and rendered corrosion-resistant, it is required that the solution material be mixed with granular refractory'coating material to produce a layer of several mils thickness on the The solution is used to seal the interstices in the coating by causing aluminum oxide to crystallize a less durable coating is provided than that produced A by either of the above methods. Aluminum is atomized by compressed air or by some mechanical device by which it is forced through a nozzle at high velocity and is impinged upon a surface to be treated. The droplets of molten aluminum become covered with a superficial film of aluminum oxide and are flattened by the impact on the surface of the article so that a series of tiny, overlapping scales are provided. The coating may then be diffused into the article by heating the article to incandescent temperature.

the neighborhood of 800 C.

L1 each of the above processes, corrosion-resistance is attained without altering the dimensions of the article. A superficial layer of material does not remain on the substrate, but rather diffuses into the substrate and renders it chemically passive.

It is also known to coat substrate materials with an enveloping layer of corrosion-resistant material. Thus, galvanizing, electroplating, porcelainizing, and other processes are known methods for depositing metal or refractory materials on substrates. Refractory deposits may be subsequently sealed by being dipped in a sealing solution or may be vitrified. Such processes provide an undesirable coating layer on a substrate and are limited to use on articles which are not to be held to close dimensional tolerances.

In the process of this invention an article may be dipped in an aqueous solution at ambient room temperatures and then be heated to dull red incandescence. The solution is preferably aqueous aluminum chloride and in non-preferred embodiments may be halogen salts of aluminum, magnesium, beryllium and alloys thereof. After being dipped the article is heated momentarily until at least dull red incandescence is attained. The treatment hardens the surface and renders it passive to chemical reaction but does not affect the physical dimensions of the article as is the case when a layer of mafrom solution deposited'material between the granules. Neither the granules nor the material therebetween diffuse into the substrate. The presence of a coating layer renders precise dimensioning practice impossible, particularly when the article is of a complex shape so that the coating builds up unevenly on the substrate.

The aqueous aluminum chloride treatment of this invention renders the surface of an article more passive to corrosive materials while introducing no dimensional change in the article. In the practice of my invention, 1 first place the steel objectto be coated in an aluminum chloride solution momentarily, dry the object by atmospheric exposure and heat the object to a temperature in A steel object may be of any desired shape as, for example, a rod, sheet, or formed object such as a propeller. I have found that a steel rod of approximately one-half inch diameter may be coated by immersion in an aqueous solution of aluminum chloride for a period of from 1 to 10 seconds, although this time interval is not critical, and then heating the rod in an electric furnace for a corresponding time at 790 C. or at least until the surface of the rod attains a dull red color.

I obtain good results in coating steel sheets by immersing the sheet in an ammonia solution of aluminum chloride for several seconds, or long enough to insure thorough wetting of the sheet surfaces, drying the sheet by exposing it to atmosphereor by playing a stream of air over it, and heating the sheet with a blow torch for a time sufficient to insure that all the areas of the sheet have become a dull red, which corresponds to a sheet temperature of approximately 600 C.-800 C.

Various types of aluminum chloride solutions may be used, and I have found that the percentage of aluminum chloride may vary from 10 percent to complete saturation. Use of a solution of aluminum chloride has the advantage of thoroughly wetting the article and creating a relatively thin film which can be readily dried on heating to provide a continuous deposit of salt on the object or tool which may be further heated to produce the desired effect.

Likewise, various methods of heating the object to be coated may be used, as for example, industrial furnaces of various types, the'main requirement being that the metal obtain the above-mentioned dull red color.

The method of this invention is not restricted to use with steel and may also be practiced successfully generally, with iron and aluminum base alloys, although the iron base alloys are preferable for subsequent use in molten aluminum. It is believed that the process substantially improves the corrosion resistance and wear resistance of most metals by hardening the surface of the metals and by providing a non-reactive dense refractory material diffuse into the surface of the article.

The invention is not restricted to the use of aluminum chloride; halogen salts of magnesium, aluminum and beryllium may be used as well.

The herein described process provides a method of rendering the surface of ferrous articles passive and resistant to corrosive attack evenat elevated temperatures. The process is to be distinguished from processes where'- in a coating is provided on substrate material in a manner such that an interface is formed between two dissimilar metals or between a substrate metal and a refractory coating material. It is believed that herein the treating solution or products derived therefrom are enabled to diffuse into the surface of the article which is being treated. The product that is obtained is similar to products that are obtained by immersing metal articles in dry salt baths such as isdone in heat'treating processes, rather than to articles which have coatings bonded thereto. It is also to be distinguished from processes wherein a solution is used to bind together and fill the interstices between granules of a refractory material which is coated on a substrate. In such processes the solution to bind together the granules of refractory material overlaying the substrate and coating, thereby adding an added ingredient to the coating is not disclosed as being corrosionresistant.

The process of this invention is operable with all known ferrous metals and alloys.

While certain modifications and embodiments of the invention have been described, it is of course to be understood that there are a great number of variations which will suggest themselves to anyone familiar with the subject matter thereof and it is to be distinctly understood that this invention should not be limited except by such limitations as are clearly imposed in the appended claims.

I claim:

1. The process of rendering the surface of a ferrous metal object corrosion-resistant comprising the steps of immersing said object in an aqueous solution of a halogen salt of a metal selected from the group consisting of aluminum, magnesium, beryllium and alloys thereof, drying the article and heating it at least to dull red incandescence.

2. The process of rendering the surface of a ferrous metal object corrosion-resistant comprising the steps of providing an aqueous solution of a metal salt, said solution having a concentration from approximately 10 per- 7 cent to saturation, said metal salt being a halogen salt of a metal selected from the group consisting of aluminum, magnesium, berryllium, and alloys thereof, wetting said object with said solution, drying said object, and heating said object to at least dull red incandescence.

'3. The article of claim 2 wherein said metal salt comprises aluminum chloride.

4. A corrosion-resistant article obtained by the process of providing on the surface of a ferrous metal object at ambient temperature conditions a continuous wet film of an aqueous solution of a metal salt wherein said metal salt comprises a halogen salt of a metal selected from the group consisting of aluminum, magnesium, berryllium, andalloys thereof, drying said object, heating said object until at least dull red incandescence is attained, thereby to provide said corrosion-resistant article.

5. The process of claim 4 wherein said solution is a solution of aluminum chloride.

6. The process of rendering the surface of a ferrous metal object corrosion-resistant comprising the steps of immersing an object in an aqueous metal salt solution of halogen salt of a metal selected from the group consisting of aluminum, magnesium, berryllium and alloys thereof at ambient temperatures, drying the object and heating it to a dull red color.

7. The process of claim 6 wherein said solution is alkaline.

References Cited in the file of this patent UNITED STATES PATENTS 1,077,480 Lang Nov. 4, 1913 1,456,274 Keep May 22, 1923 2,059,280 Ruben Nov. 3, 1936 2,756,162 Garner July 24, 1956 FOREIGN PATENTS 638,374 Great Britain June 7, 1950 

1. THE PROCESS OF RENDERING THE SURFACE OF A FERROUS METAL OBJECT CORROSION-RESISTANT COMPRISING THE STEPS OF IMMERSING SAID OBJECT IN AN AQUEOUS SOLUTION OF A HALOGEN SALT OF A METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, MAGNESIUM, BERYLLIUM AND ALLOYS THEREOF, DRYING THE ARTICLE AND HEATING IT AT LEAST TO DULL RED INCANDESCENCE. 